1. Field of the Invention
This invention relates to a design of a control knob for a control device such as a rotary switch, and particularly to one having a two-step function; as for example, a push-to-turn action.
2. Description of the Prior Art
A standard multiple rotary switch has a shaft that carries a knob with a handle for setting the switch in one of a plurality of switch settings, including an OFF position. From the point of view of safety in the use of kitchen appliances, it is important that the easily accessible switches not be capable of being set to an ON position inadvertently. For example, the selector switches that control the electric surface heating units of the cooktop of an electric range are usually accessible to small children. If a soiled frying pan, or a dishcloth, or a food package, were resting on the surface unit and the selector switch was accidentally moved to an ON position, the surface unit would be energized and a fire might be started before the situation could be corrected.
One solution is to design those switches, which are accessible and may become potential safety hazards, with a two-step function so it is difficult to inadvertently turn the switch ON.
This two-step function could be built into the switch mechanism at a cost increase, but, instead, the present invention contemplates simply modifying the control knob, at much less expense, to provide the two-step function.
An example of a standard control knob is shown in the Keeling/Baughman U.S. Pat. No. 3,176,541, which is assigned to the present assignee. This particular knob is for use with an oven thermostat and the knob is furnished with an adjusting means for recalibrating the thermostat.
An example of a two-step control knob is shown in the Marrapese U.S. Pat. No. 2,797,592, which shows a complex multi-part design of knob for an appliance switch or gas valve with a knob handle that turns freely and is inoperative unless it is first pushed and then turned. The knob has a clutch plate which must be engaged by pushing in on the handle before the turning of the handle becomes effective to operate the switch or valve.
Another example of a two-step control knob is shown in the Beare U.S. Pat. No. 3,227,826, which shows a push-to-turn timer switch where clutch teeth are provided on the timer knob which must engage with clutch teeth fixed with respect to the timer rotor shaft before any manual adjustment of the angular position of the cam discs is possible.
The principal object of the present invention is to provide a control device with a two-step feature before it can be set from an OFF position to any one of its ON positions by providing the control knob of the device with a releasable locking means for the OFF position.
A further object of the present invention is to provide a control device of the class described wherein the control knob is fixed from rotation while in the normal OFF position.
A further object of the present invention is to provide a control device of the class described where the control knob has a push-to-turn action at the OFF setting.
A further object of the present invention is to provide a control device of the class described where the two-step control knob can be used on a standard control device; hence, the two-step feature is external of the control device.